Proton-conducting ceramic fuel cell architecture

ABSTRACT

A method of manufacturing a proton-conducting fuel cell includes assembling a green anode-electrolyte half-cell by forming an anode substrate layer having an upper surface and a lower surface, forming an anode functional layer on the upper surface of the anode substrate layer, forming an electrolyte layer on an upper surface of the anode functional layer, and forming a stress balancing layer on the lower surface of the anode substrate layer. The method further includes positioning the green anode-electrolyte half-cell on kiln furniture inside a sintering kiln and sintering the green anode-electrolyte half-cell using SSRS to an anode-electrolyte half-cell.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of and priority to U.S.Provisional Patent Application No. 63/244,054 filed Sep. 14, 2021, whichis hereby incorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with Government Support under CooperativeAgreement DE-AR0000493 awarded by the United States Department ofEnergy. The Government has certain rights in the invention.

BACKGROUND

The present application relates generally to the field ofproton-conducting ceramic fuel cell (PCFC) systems and, moreparticularly, the manufacture of PCFC systems at a commercially viablesize and cost.

Generally, a fuel cell includes an anode, a cathode, and an electrolytelayer that together drive chemical reactions to produce electricity.Specifically, a PCFC is a solid electrochemical cell comprising aceramic electrolyte sandwiched between a porous anode and porouscathode. Fuel, such as hydrogen gas or hydrocarbon gas, is supplied tothe anode. The anode causes the hydrogen atom electrons to dissociatefrom the hydrogen protons. The protons travel across theproton-conducting electrolyte to the cathode, where they bond tooxidants, such as oxygen gas. The electrons travel through an externalcircuit from the anode to the cathode to generate electric power.

PCFC systems may be preferable to Solid Oxide Fuel Cell (SOFC) systemsin certain circumstances, because they can provide enhanced performanceat lower operating temperatures, resulting in lower operating costs andfewer material compatibility challenges. While SOFCs generally operateat temperatures in the range of 600-1000° C., PCFCs can provide goodperformance under 600′C.

PCFCs are traditionally manufactured using high-temperature calcinationand sintering processes that require relatively long processing times,which in turn can contribute to a relatively high production cost.Additionally, prior PCFC production techniques that utilized solid statereaction sintering (SSRS) presented issues such as bonding of thematerials to kiln furniture and/or warpage of the parts due to highshrinkage compared to conventional sintering processes. Accordingly, itwould be advantageous to develop a PCFC manufacturing process thatallows for cells of commercially viable size to be manufactured using alower-temperature sintering process.

SUMMARY

In some embodiments of the present disclosure, a method of manufacturinga PCFC includes assembling a green anode-electrolyte half-cell byforming an anode substrate layer having an upper surface and a lowersurface, forming an anode functional layer on the upper surface of theanode substrate layer, forming an electrolyte layer on an upper surfaceof the anode functional layer, and forming a stress balancing layer onthe lower surface of the anode substrate layer. The method furtherincludes positioning the green anode-electrolyte half-cell on kilnfurniture inside a sintering kiln and sintering the greenanode-electrolyte half-cell using SSRS to an anode-electrolytehalf-cell.

In some aspects of the method, the method further comprises forming acathode layer on an upper surface of the electrolyte and cathodesintering the anode-electrolyte half-cell and cathode layer.

In some aspects, the assembling of the green anode-electrolyte half-cellfurther comprises forming a coarse NiO layer on a lower surface of thestress balancing layer such that, when the green anode-electrolytehalf-cell is positioned on the kiln furniture, the stress balancinglayer does not directly contact the kiln furniture. In some aspects thecoarse NiO layer may comprise NiO powder with average particle sizeabove about 20 micrometers and below about 2.0 mm. The NiO powder mayhave an average particle size of about 60 micrometers.

In some aspects, the coarse NiO layer may be brushed off aftersintering. In other aspects, the coarse NiO layer may be reduced tonickel metal by operating the PCFC.

In some aspects, the method may include forming a layer of coarse NiOpaste on the kiln furniture such that the anode-electrolyte half-cell isnot in contact with the kiln furniture. In some aspects, the method mayinclude placing a sheet of yttria paper between the anode-electrolytehalf-cell and the kiln furniture such that the anode-electrolytehalf-cell is not in contact with the kiln furniture.

In other embodiments of the present disclosure, a PCFC is provided whichcomprises an anode substrate layer comprising an upper surface and alower surface, an anode functional layer coupled to the upper surface ofthe anode substrate layer, an electrolyte layer coupled to an uppersurface of the anode functional layer, and a stress balancing layercoupled to the lower surface of the anode substrate layer.

In some aspects, the PCFC further comprises a cathode layer coupled toan upper surface of the electrolyte layer.

In some aspects, the PCFC further comprises a coarse NiO layer coupledto a lower surface of the stress balancing layer. In some aspects, thePCFC includes a layer of nickel metal coupled to a lower surface of thestress balancing layer, the layer of nickel metal formed by heating alayer of coarse NiO

In some aspects, the stress balancing layer may be more than about Sumthick and less than about 100 micrometers thick.

In other embodiments of the present disclosure, a PCFC is provided whichcomprises an anode substrate layer comprising an upper surface and alower surface, an anode functional layer coupled to the upper surface ofthe anode substrate layer, an electrolyte layer coupled to an uppersurface of the anode functional layer, and a coarse NiO layer forming alower surface of the proton-conducting fuel cell.

In some aspects, the coarse NiO layer may comprise NiO powder with anaverage particle size above about 20 micrometers and below about 2.0 mm,and preferably about 60 micrometers.

It will be appreciated that these and other features and/or aspectsmaybe used in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

A clear conception of the advantages and features constituting thepresent disclosure, and of the construction and operation of typicalmechanisms provided with the present disclosure, will become morereadily apparent by referring to the exemplary, and thereforenon-limiting, embodiments illustrated in the drawings accompanying andforming a part of this specification, wherein like reference numeralsdesignate the same elements in the several views, and in which:

FIG. 1A is a schematic representation of a typical PCFCanode-electrolyte half-cell that has warped during a conventional SSRSprocess.

FIG. 1B is a schematic representation of a PCFC anode-electrolytehalf-cell including a stress balancing layer, according to an exemplaryembodiment.

FIG. 1C is a schematic representation of a PCFC anode-electrolytehalf-cell on kiln furniture inside a sintering kiln during aconventional SSRS process that has warped due to the cell materialsreacting with the kiln furniture.

FIG. 1D is a schematic representation of a PCFC anode-electrolytehalf-cell, including a coarse NiO layer, on kiln furniture inside asintering kiln during the SSRS process.

FIG. 2 illustrates flow diagram of an exemplary embodiment of preparinga PCFC anode-electrolyte half-cell.

FIG. 3A is a schematic representation of a PCFC anode-electrolytehalf-cell on kiln furniture inside a sintering kiln during the SSRSprocess with a layer of coarse NiO paste applied to the kiln furniture.

FIG. 3B is a schematic representation of a PCFC anode-electrolytehalf-cell on kiln furniture inside a sintering kiln during the SSRSprocess with a layer of coarse NiO paste applied to the kiln furnitureand a coarse NiO layer applied to the half-cell.

FIG. 3C is a schematic representation of a PCFC anode-electrolytehalf-cell on kiln furniture inside a sintering kiln during the SSRSprocess with a sheet of yttria paper between the half-cell and the kilnfurniture.

FIG. 4A is a graph of voltage and power density readings at variouscurrent densities and temperatures of a first test PCFC containing astress balancing layer and sintered with a coarse layer of NiO on thekiln furniture, according to an embodiment of the invention.

FIG. 4B is a graph of voltage and power density readings during a repeattest at various current densities and temperatures of the first PCFCcontaining a stress balancing layer and sintered with a coarse layer ofNiO on the kiln furniture, according to an embodiment of the invention.

FIG. 4C is a graph of voltage and power density readings at variouscurrent densities and temperatures of a second test PCFC containing astress balancing layer and sintered with a layer of yttria paper betweenthe half-cell and kiln furniture, according to an embodiment of theinvention.

FIG. 5 is a graph of voltage and power density readings at variouscurrent densities and temperatures of a solid oxide fuel cell notmanufactured according to an embodiment of the invention, shown forcomparison to the embodiments of the invention.

FIG. 6A is a graph of steady-state voltage readings at 700° C. and 0.34A/cm² of the first test PCFC containing a stress balancing layer andsintered with a coarse layer of NiO on the kiln furniture, according toan embodiment of the invention.

FIG. 6B is a graph of steady-state voltage readings at 550° C. and 0.2A/cm² of the second test PCFC containing a stress balancing layer andsintered with a layer of yttria paper between the half-cell and kilnfurniture, according to an embodiment of the invention.

FIG. 7 is a graph of steady-state voltage readings at 550V and 0.2 A/cm′of a of a solid oxide fuel cell not manufactured according to anembodiment of the invention, shown for comparison to the embodiments ofthe invention.

FIG. 8 is a scanning electron microscope (SEM) image of a cross-sectionof the upper layers of a PCFC anode-electrolyte half-cell according toan exemplary embodiment.

FIG. 9 is an SEM image of a cross-section of the upper layers of a PCFCaccording to an exemplary embodiment.

FIG. 10 is an SEM image of a cross-section of a PCFC containing a stressbalancing layer according to an exemplary embodiment.

FIG. 11 is an SEM image of a cross-section of a PCFC containing a stressbalancing layer according to an exemplary embodiment.

FIG. 12 is an SEM image of a cross-section of the lower layers of a PCFCcontaining a stress balancing layer and a coarse NiO layer according toan exemplary embodiment.

The foregoing and other features of the present disclosure will becomeapparent from the following description and appended claims, taken inconjunction with the accompanying drawings. Understanding that thesedrawings depict only several embodiments in accordance with thedisclosure and are therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe figures, can be arranged, substituted, combined, and designed in awide variety of different configurations, all of which are explicitlycontemplated and made part of this disclosure.

PCFCs may be manufactured using a lower temperature sintering processthrough the use of solid-state reactive sintering (SSRS). The use ofSSRS allows for the sintering of anode-electrolyte half-cells attemperatures of about 1450° C. or less, compared to temperatures as highas 1700° C. for traditional PCFC sintering.

Production of PCFCs using SSRS includes a first solid-state reactivesintering of the anode-electrolyte half-cell containing a thin layer ofanode substrate, an anode functional layer, and an electrolyte layer.During the SSRS step, the anode substrate layer, generally the bottomlayer, may be placed directly on the kiln furniture inside the sinteringkiln. The layers bond during SSRS process to form the half-cell. PCFCfabrication may be completed by screen printing a layer of cathode ontothe upper surface of the electrolyte layer and conventionally sinteringthe cell a second time at a lower temperature, about 800-1000° C., aprocess called cathode sintering.

While the SSRS method has been successful in producing small test cells,or button cells, fabrication of PCFCs at a commercially viablesize—about 81 cm² active electrode area or larger—poses additionalproblems. First, fuel cells sintered using SSRS shrink up to 1.5 timesas much as conventionally sintered cells, causing the cell to warpduring processing due to the inconsistent shrink rates in the layers.Second, the carbonates and oxides used to produce the barium zirconatesin the anode substrate layer, which is in contact with the furnitureinside the sintering kiln, react strongly with the kiln furniturematerial, generally zirconia or silicon carbide. The reaction with thekiln furniture causes the half-cells to deform and break due to thelarge surface area in contact with the kiln furniture. For smallerbutton cells, an additional layer of electrolyte can be bonded to thelower surface of the anode substrate, i.e. the surface opposite theanode functional layer. This layer can be ground off after sintering toexpose the anode substrate for use in a test cell. Because there is lessshrinkage due to the size of the button cells, the reaction between thehalf-cell and the kiln furniture is less likely to be destructive.However, this solution is not viable for larger cells because of thelarger contact area between the half-cell and the kiln furniture.

The present disclosure discusses the production of PCFCs that contain astress balancing layer coupled to the bottom surface of the anodesubstrate layer as well as methods of fabricating such a PCFC. Variousfabrication methods include steps to prevent the reaction of the anodesubstrate with the sintering kiln furniture using a coarse layer of NiOpaste or a sheet of yttria paper between the half-cell and kilnfurniture. These methods overcome previous limitations which preventedthe production of PCFCs of commercially viable size due to the PCFCwarping during sintering and bonding to the kiln furniture, causingdeformation and breakage.

PCFCs made according to the embodiments described herein havedemonstrated peak power densities of about 521 mW/cm² when tested at anoperating temperature of 550′C, which is more than double the powerdensity of typical solid oxide fuel cells at that relatively lowtemperature.

FIG. 1A is a representation of a typical PCFC anode-electrolytehalf-cell 100 a that does not include a stress balancing layer. Thehalf-cell 100 a shown has warped during sintering due to the lack of astress balancing layer. The anode substrate layer 110 is formed from theanode substrate base material, generally a mixture of barium andzirconium oxides and/or carbonates and nickel oxide, which is combinedwith binders and solvents to form a paste. The paste is then laid out ina thin (between approximately 0.2 and 2.0 millimeters (mm)) layer,typically using tape casting, and dried. Note that the various ceramicmaterials that make up the completed cell are in the form of oxide andcarbonate precursors of the ceramic components prior to sintering, andform barium zirconate ceramics during the sintering process. Next, theanode functional layer 120 is formed from the anode functional layer 120base material, which is mixed with binders and solvents to form a pasteand screen printed, doctor bladed, or painted onto the dried anodesubstrate layer 110. The anode functional layer 120 is generally amixture of a barium and zirconium oxides and/or carbonates and NiO witha thickness of between approximately 5 and 50 micrometers. Finally, theelectrolyte layer 130 is formed from the electrolyte base material,which is combined with binders and solvents to form a paste and screenprinted, doctor bladed, or painted onto the dried anode functional layer120. The electrolyte layer 130 is generally a mixture of barium andzirconium oxides and/or carbonates having a thickness of betweenapproximately 5 and 50 micrometers. These layers are sintered togetherusing SSRS to form the PCFC anode-electrolyte half-cell 100 a containingan anode substrate layer 110, an anode functional layer 120, and anelectrolyte layer 130. A cathode layer may then be sintered to thehalf-cell 100 a on top of the electrolyte layer 130 at lowertemperatures in a separate step to complete the cell.

During sintering, anode-electrolyte half-cells shrink as the basematerials densify into ceramic. To fabricate an ideal anode-electrolytehalf-cell, the electrolyte layer 130 is sintered to a fully dense state,while the anode functional layer 120 is slightly more porous with a finemicrostructure, and the anode substrate layer 110 is even more porouswith a coarser microstructure. Thus, the electrolyte layer 130experiences the most shrinkage, the anode functional layer 120 slightlyless shrinkage, and the anode substrate layer 110 the least shrinkage.

Due to the differing rates of shrinkage, as well as temperaturedifferentials in the half-cell and differences in the stress state inthe middle of the half-cell (fully constrained) compared to the edges ofthe cell (partially constrained), half-cells can warp during sintering,as shown in FIG. 1A. Compared to a traditional fuel cell sinteringprocess, there is additional chemical shrinkage during SSRS as thecarbonates and oxides are converted into the final perovskite phase.While excessive shrinkage does not have a strong effect on small buttoncells made using SSRS, large-area, thin half-cells that are required forcommercial PCFC operation may be so warped as to require multipletime-consuming and expensive ironing steps, or may be entirely unusable.

FIG. 1B is a representation of an exemplary embodiment of a PCFCanode-electrolyte half-cell 110 b that includes a stress balancing layer140. The stress balancing layer 140 is made from a material similar tothat of the anode functional layer 120 and may be between approximately5 and 100 micrometers thick. In some embodiments, the stress balancinglayer 140 may be approximately the same thickness as the anodefunctional layer 120. The stress balancing layer 140 is formed from thestress balancing layer base material, a material similar to or the sameas the anode functional layer base material, which is combined withbinders and solvents to form a paste and screen printed, doctor bladed,or painted on to the lower surface of the anode substrate layer 110,i.e. the surface opposite the anode functional layer 120. The stressbalancing layer 140 roughly matches the rate of shrinkage of the anodefunctional layer 120 and electrolyte layer 130, preventing or reducingthe amount of warping in the PCFC during SSRS by balancing themismatched shrinkage rates between the anode substrate layer 110, theanode functional layer 120, and electrolyte layer 130. After theanode-electrolyte half-cell 100 b is fabricated according to the variousembodiments described herein, a complete PCFC may be fabricated byapplying a cathode layer to the upper surface of the electrolyte layer130 (i.e., the surface opposite the anode functional layer 120), andsintering again at a lower temperature in the range of betweenapproximately 800 and 1000 degrees Celsius. This step is called cathodesintering. FIG. 9 illustrates the microstructure of a cathode layerafter it has been sintered to an anode-electrolyte half-cell.

FIG. 1C shows a PCFC anode-electrolyte half-cell 100 b, including astress balancing layer 140 as described above, on the kiln furniture 190inside the sintering kiln 180. The stress balancing layer 140 is indirect contact with the kiln furniture 190, with the anode substratelayer 110 on top of the stress balancing layer 140, the anode functionallayer 120 on top of the anode substrate layer 110 and the electrolytelayer 130 on top of the anode functional layer 120. The direct contactof the half-cell 100 b with the kiln furniture 190 may cause the stressbalancing layer 140 to react with and bond to the kiln furniture 190during sintering. This may cause the half-cell 100 b to warp and/orcrack, which may require the half-cell 100 b to be ironed flat prior touse or may render the half-cell 100 b unusable altogether. In ahalf-cell with no stress balancing layer (e.g., half-cell 100 a), theanode substrate layer 110 may be in direct contact with the kilnfurniture 190 during firing and may similarly react with the kilnfurniture 190. Thus, separation between the stress balancing layer 140or anode substrate layer 110 and the kiln furniture 190 may be requiredto prevent or reduce the amount of warping and cracking of thehalf-cell.

A layer of appropriate material between the kiln furniture and thehalf-cell may be used to prevent the cell materials from reacting withthe kiln furniture. Kiln furniture is generally made of zirconia orsilicon carbide which can withstand the extreme temperatures inside thesintering kiln. The material used to prevent the cell materials fromreacting with and bonding to the kiln furniture must also be able towithstand these temperatures. In order to overcome the cell materials'reacting with and bonding to the kiln furniture, extensiveexperimentation was done with various materials placed between the kilnfurniture and the cell. Some of the materials tested include zirconiafoam, zirconia plate, zirconia fiber paper, dense alumina plate, porousalumina plate, alumina fiber paper, silicon carbide plate, and NiOpowder finer than 20 micrometers. In each case, the cell either stillreacted with the kiln furniture, reacted with the test material,cracked, warped, or was completely destroyed. Two solutions wereeventually discovered: (i) a layer of coarse NiO powder paste appliedbetween the half-cell and the kiln furniture, either on the kilnfurniture, on the cell itself, or both, and (ii) yttria paper placedbetween the half-cell and the kiln furniture.

FIG. 1D shows a PCFC anode-electrolyte half-cell 100 c with a coarse NiOlayer 150 according to an embodiment of the present disclosure. Thecoarse NiO layer 150 is formed from the coarse NiO layer base material,coarse NiO powder with an average particle size above about 20micrometers and below about 2.0 mm, which is combined with binders andsolvents to form a paste. In one successful test cell according to anexemplary embodiment, the average particle size of the NiO powder wasabout 60 micrometers. The coarse NiO layer paste loosely sinters duringSSRS and forms a coarse microstructured layer, and prevents or reducesthe reaction between the kiln furniture and the oxides and carbonatesused to make barium zirconates of the half-cell. The coarse NiOparticles of the coarse NiO layer 150 do not bond or react strongly withthe kiln furniture. Thus, the coarse NiO layer 150 prevents or reduceswarpage and cracking of the half-cell 100 c due to reactions with thekiln furniture and the stress balancing layer 140 prevents or reduceswarpage due to mismatched shrink rates.

FIG. 8 is an image from a scanning electron microscope showing themicrostructure of a cross-section of the upper layers of a PCFCanode-electrolyte half-cell manufactured with a stress-balancing layer(e.g., stress balancing layer 140) and a sacrificial layer (e.g., coarseNiO layer 150 that may be removed or converted to nickel metal)according to an exemplary embodiment. The stress-balancing layer andsacrificial layer have prevented the half-cell from warping or cracking.FIG. 9 is an image from a scanning electron microscope showing themicrostructure of the upper layers of a PCFC after a cathode layer hasbeen sintered to an anode-electrolyte half-cell according to anexemplary embodiment. FIGS. 10 and 11 are images from a scanningelectron microscope showing the microstructure of a PCFC with astress-balancing layer according to an exemplary embodiment. FIG. 12 isan image from a scanning electron microscope showing the microstructureof the lower layers of a PCFC with a stress-balancing layer and asacrificial layer according to an exemplary embodiment.

Various embodiments of the present disclosure include methods ofproducing PCFCs as described above. FIG. 2 illustrates an embodiment ofa method of producing a PCFC of commercially viable size. At step 210,anode substrate paste is tape cast or otherwise deposited to form theanode substrate layer 110. At step 220, anode functional layer paste isscreen printed or otherwise applied onto the top of the anode substratelayer 110 to form the anode functional layer 120. At step 230,electrolyte paste is screen printed or otherwise applied onto the top ofthe anode functional layer 120 to form the electrolyte layer 130. Atstep 240, stress balancing layer paste is screen printed or otherwiseapplied onto the bottom of the anode substrate layer 110 to form thestress balancing layer 140. As described above, the stress balancinglayer 140 is coupled to the anode substrate to prevent or reduce bowing,warping, and cracking of the half-cell 100 c during sintering. At step250, coarse NiO layer paste is screen printed or otherwise applied ontothe bottom surface of the stress balancing layer 140 (i.e., the surfaceopposite the anode substrate layer 110) to form the coarse NiO layer150. These layers form a green half-cell that may not warp due tomismatched shrinkage rates or due to reaction with the kiln furniture190 during sintering. In other exemplary embodiments, steps 210-250 maybe completed in different orders. For example, the stress balancinglayer 140 may be applied to the bottom of the anode substrate layer 110before the anode functional layer 120 and electrolyte layer 130 areapplied.

At step 260 in FIG. 2 , the green half-cell is sintered in a sinteringkiln 180 using SSRS at approximately 1450° C. to form the half-cell 100c containing a stress balancing layer 140 and a coarse NiO layer 150.The arrangement of the half-cell 100 c during the sintering step 260 isshown in FIG. 1D. The coarse NiO layer 150 is a coarse layer of NiOloosely coupled to the stress balancing layer 140. At step 270, thecoarse NiO layer is manually brushed off of or otherwise removed fromthe half-cell 100 c. At step 280, the cathode paste is screen printed orotherwise applied onto the top surface of the electrolyte layer 130,i.e. the surface opposite the anode functional layer 120, to form thecathode layer. At step 290, the cell is sintered again with the cathodelayer at a lower temperature such as 900° C. (cathode sintering) to formthe completed PCFC.

In other exemplary embodiments, the coarse NiO layer 150 may be designedsuch that it remains attached to the cell. During PCFC operation, thecoarse NiO layer 150 that remains attached may be reduced to nickelmetal, which may be conductive and compatible with the other cellmaterials and may not interfere with the operation of the cell.

In some embodiments, as shown in FIG. 3A, a layer of coarse NiO paste155 may be applied directly to the kiln furniture 190 rather than to thehalf-cell. After sintering, the NiO layer on the kiln furniture 190 isgenerally reduced to a loose powder bed. The NiO can be swept up andreprocessed into a paste for subsequent firings. Some of the NiO thatwas applied to the kiln furniture 190 may bond to the PCFC after firing,and can be manually brushed off.

In some embodiments, a coarse layer of nickel oxide may be applied bothto the anode-electrolyte half-cell 100 c and to the kiln furniture 190.FIG. 3B shows the arrangement of a half-cell 100 c with a coarse NiOlayer 150 in a sintering kiln 180 with a layer of coarse NiO paste 155applied to the kiln furniture 190. As in the embodiments describedabove, the NiO can be brushed off the kiln furniture 190 and thehalf-cell 100 c, or may be brushed off the kiln furniture 190 and remainon the half-cell 100 c, where it will be reduced to nickel metal duringPCFC operation.

In other exemplary embodiments, as shown in FIG. 3C, the PCFCanode-electrolyte half-cell 100 b is sintered without the use of acoarse NiO layer on either the half-cell or the kiln furniture. Instead,yttria paper 160 is placed between the half-cell 100 b and the kilnfurniture 190 to prevent them from reacting with and bonding to eachother. The yttria paper 160 may be reused for sintering multiple cellsbefore needing to be replaced due to degradation.

Various embodiments include using yttria paper 160 or a coarse NiO layer150, 155 between the PCFC materials and the kiln furniture 190 withoutthe use of a stress balancing layer 140. Button cells may be producedwith this method, and future development in PCFC fabrication may obviatethe need for a stress balancing layer 140.

EXAMPLE

A first test cell with an active electrode area of 81 cm² was producedin which a layer of coarse NiO paste was applied to the kiln furnitureprior to sintering. Voltage and power density were measured during afirst test at various operating temperatures and current densities, andthe measurements are shown in FIG. 4A. FIG. 4B shows the results from arepeat test performed with the same cell. Operating at 550 degreesCelsius (a relatively low temperature for most fuel cells of this type)the PCFC had a peak power density of approximately 521 mW/cm². FIG. 6Ashows the results of a steady-state hold test of the first test cell.The cell was held at a temperature of 700 degrees Celsius and a currentdensity of 0.34 A/cm² while voltage was measured over an extendedduration. The cell voltage measured between about 0.80V and 0.93V overthe course of about 400 hours.

A second test cell with an active electrode area of 81 cm² was producedaccording to an embodiment of the invention in which yttria paper isplaced between the half-cell and kiln furniture during sintering.Voltage and power density of the second test cell were measured atvarious operating temperatures and current densities, and themeasurements are shown in FIG. 4C. At 550 degrees Celsius, the secondtest cell performed as well as the first, also reaching a peak powerdensity of about 521 mW/cm². FIG. 6B shows the results of a steady-statehold test performed on the second test cell at a temperature of 550degrees Celsius and a current density of 0.2 A/cm². The cell voltagemeasured between about 0.89V and 0.84V over the course of about 250hours.

A solid oxide fuel cell, not according to an embodiment of thisdisclosure, was tested under similar conditions for comparison to thePCFC test cells. Voltage and power density were measured during a firsttest at various operating temperatures and current densities, and themeasurements are shown in FIG. 5 . The solid oxide fuel cell had a peakpower density at 550 degrees Celsius of only about 200 mW/cm², less thanhalf that of the PCFC test cells produced according to the embodimentsof the invention. FIG. 7 shows the results of a steady-state hold testperformed on the solid oxide fuel cell. The solid oxide fuel cellvoltage measured between about 0.70V and 0.67V over the course of about1100 hours, more than 0.1V lower than the second PCFC test cell testedat the same temperature and current density (i.e., 550 degrees Celsiusand 0.2 A/cm²). The test data shows that the PCFC cells producedaccording to embodiments of the present application outperform solidoxide fuel cells at the relatively low temperature of 550 degreesCelsius.

Notwithstanding the embodiments described above in FIGS. 1-12 , variousmodifications and inclusions to those embodiments are contemplated andconsidered within the scope of the present disclosure.

It is also to be understood that the construction and arrangement of theelements of the systems and methods as shown in the representativeembodiments are illustrative only. Although only a few embodiments ofthe present disclosure have been described in detail, those skilled inthe art who review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter disclosed.

Accordingly, all such modifications are intended to be included withinthe scope of the present disclosure. Any means-plus-function clause isintended to cover the structures described herein as performing therecited function and not only structural equivalents but also equivalentstructures. Other substitutions, modifications, changes, and omissionsmay be made in the design, operating conditions, and arrangement of thepreferred and other illustrative embodiments without departing fromscope of the present disclosure or from the scope of the appendedclaims.

Furthermore, functions and procedures described above may be performedby specialized equipment designed to perform the particular functionsand procedures. The functions may also be performed by general-useequipment that executes commands related to the functions andprocedures, or each function and procedure may be performed by adifferent piece of equipment with one piece of equipment serving ascontrol or with a separate control device.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable,” to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

References herein to the positions of elements (e.g., “top,” “bottom,”“in front,” “behind,” “above,” “below”) are merely used to describe theorientation of various elements in the FIGURES. It should be noted thatthe orientation of various elements may differ according to otherexemplary embodiments, and that such variations are intended to beencompassed by the present disclosure.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Similarly, unless otherwise specified, the phrase “basedon” should not be construed in a limiting manner and thus should beunderstood as “based at least in part on.” Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances, where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.” Further, unless otherwisenoted, the use of the words “approximate,” “about,” “around,”“substantially,” etc., mean plus or minus ten percent. Moreover,although the figures show a specific order of method operations, theorder of the operations may differ from what is depicted. Also, two ormore operations may be performed concurrently or with partialconcurrence. Such variation will depend on the software and hardwaresystems chosen and on designer choice. All such variations are withinthe scope of the disclosure. Likewise, software implementations could beaccomplished with standard programming techniques with rule based logicand other logic to accomplish the various connection operations,processing operations, comparison operations, and decision operations.

What is claimed is:
 1. A method of manufacturing a proton-conductingfuel cell (PCFC), the method comprising: assembling a greenanode-electrolyte half-cell, the assembling comprising: forming an anodesubstrate layer comprising an upper surface and a lower surface oppositethe upper surface; forming an anode functional layer on the uppersurface of the anode substrate layer; forming an electrolyte layer on anupper surface of the anode functional layer; and forming a stressbalancing layer on the lower surface of the anode substrate layer;positioning the green anode-electrolyte half-cell on kiln furnitureinside a sintering kiln; and sintering the green anode-electrolytehalf-cell in the sintering kiln using solid state reaction sintering toform an anode-electrolyte half-cell.
 2. The method of claim 1, furthercomprising: forming a cathode layer on an upper surface of theelectrolyte layer; and cathode sintering the anode-electrolyte half-celland the cathode layer.
 3. The method of claim 1, the assembling of thegreen anode-electrolyte half-cell further comprising forming a coarseNiO layer on a lower surface of the stress balancing layer such that,when the green anode-electrolyte half-cell is positioned on the kilnfurniture, the stress balancing layer does not directly contact the kilnfurniture.
 4. The method of claim 3, wherein the coarse NiO layercomprises NiO powder with an average particle size above about 20micrometers and below about 2.0 mm.
 5. The method of claim 3, whereinthe coarse NiO layer comprises NiO powder with an average particle sizeof about 60 micrometers.
 6. The method of claim 3 further comprisingbrushing the coarse NiO layer off the anode-electrolyte half-cell. 7.The method of claim 3 further comprising reducing the coarse NiO layerto nickel metal by operating the PCFC.
 8. The method of claim 3 furthercomprising forming a layer of coarse NiO paste on the kiln furnituresuch that, when the green anode-electrolyte half-cell is positioned onthe kiln furniture, the green anode-electrolyte half-cell does notdirectly contact the kiln furniture.
 9. The method of claim 1 furthercomprising forming a layer of coarse NiO paste on the kiln furnituresuch that, when the green anode-electrolyte half-cell is positioned onthe kiln furniture, the green anode-electrolyte half-cell does notdirectly contact the kiln furniture.
 10. The method of claim 1 furthercomprising positioning a layer of yttria paper between the greenanode-electrolyte half-cell and the kiln furniture such that the greenanode-electrolyte half-cell does not directly contact the kilnfurniture.
 11. A proton-conducting fuel cell comprising: an anodesubstrate layer comprising an upper surface and a lower surface; ananode functional layer coupled to the upper surface of the anodesubstrate layer; an electrolyte layer coupled to an upper surface of theanode functional layer; and a stress balancing layer coupled to thelower surface of the anode substrate layer.
 12. The proton-conductingfuel cell of claim 11, further comprising a cathode layer coupled to anupper surface of the electrolyte layer.
 13. The proton-conducting fuelcell of claim 11, further comprising a coarse NiO layer coupled to alower surface of the stress balancing layer.
 14. The proton-conductingfuel cell of claim 11, further comprising a layer of nickel metalcoupled to a lower surface of the stress balancing layer, the layer ofnickel metal formed by heating a layer of coarse NiO.
 15. Theproton-conducting fuel cell of claim 11, wherein the stress balancinglayer comprises base materials as and the anode functional layer alsoincludes the base materials.
 16. The proton-conducting fuel cell ofclaim 15 wherein the stress balancing layer and the anode functionallayer are approximately the same thickness.
 17. The proton-conductingfuel cell of claim 11, wherein the stress balancing layer is more thanabout 5 micrometers thick and less than about 100 micrometers thick. 18.A proton-conducting fuel cell comprising: an anode substrate layercomprising an upper surface and a lower surface; an anode functionallayer coupled to the upper surface of the anode substrate layer; anelectrolyte layer coupled to an upper surface of the anode functionallayer; and a coarse NiO layer forming a lower surface of theproton-conducting fuel cell.
 19. The proton-conducting fuel cell ofclaim 18, wherein the coarse NiO layer comprises NiO powder with anaverage particle size above about 20 micrometers and below about 2.0 mm.20. The proton-conducting fuel cell of claim 18, wherein the coarse NiOlayer comprises NiO powder with an average particle size of about 60micrometers.